1. Field of Invention
The present invention relates generally to apparatuses and methods for dam reinforcement and rehabilitation, and more particularly to a method and apparatus for stopping tunnel erosion resulting from piping in dikes and dams by injecting two-component polymeric material to form a hydra-insensitive expanding polymer block inside the piping channels.
2. Background
The safety of hydraulic infrastructures such as reservoirs is one of the top priority safety concerns. If a reservoir collapses, it could cause heavy damages to properties or even casualties. Piping, a common hazer for dams and dikes, is a progressive formation of an underground erosion tunnel between the upstream and the downstream sides in a dam. It occurs when small granules in non-cohesive soil move or are moved out by water flow through the pores of big granules under seepage. The granules move to form interstices, then the interstices gradually expand and form irregular piping channel eventually. It occurs at the seepage outlet or inside the soil. As the piping magnitude increases, the soil continuously drains and the interstice diameter gradually expands, and the interstice depth gradually extends into the dike. Once the existing interstices connect with each other, the soil will lose faster, which further causes the interstices in dike to collapse and eventually the dike may collapse as well.
The conventional treatment methods for piping are as follows:
The Loaded Filter Method. This method comprises these steps: throwing flexible materials such as plugs or fabrics into the piping channel to reduce the flow of water current; blocking the entrance of piping tunnel with bags filled with soil and rock; throwing in thick clays along the side of the dike, and at the same time setting up the surround well near the outlet of piping tunnel to guide the water flow to make sure that the current does not further damage the outlet, does not carry sand in the water, and the seepage returns back to the normal level.
The Cement-Clay Paste Grouting Method. This method uses grouting pressure to squeeze cement-clay paste into the gaps, cracks or caves and then forms in coagulation. As the cement-clay paste flows in the piping channel and as distance extends, the grouting pressure gradually reduces while the frictional resistance gradually increases. As the flow speed gradually reduces, the cement-clay paste begins to accumulate and eventually blocks up the piping channel. The rationale of this method is that the agglutinating property of cement-clay paste and the property of the sand and soil in piping tunnels are similar in their elastic modulus, therefore, the cement clay paste grout can perform the blocking.
Though widely used, the above methods have several known drawbacks and deficiencies.
Time Consuming and Labor Intensive. Once a piping spot gets noticed, the dike should be treated as an emergency and must be reinforced immediately. But the conventional methods usually take too long to be implemented.
Insufficient Treatment. Neither of the conventional methods mentioned above is able to offer an adequate solution. The loaded filter method is mainly used to block the inlet and the outlet ends of a tunnel. It is unable to reach inside the tunnel to block the entire piping channel. As such, the integrity of dike suffers, for example, another piping problem may well be likely to take place at exactly the same spot over time. As for the cement-clay paste grouting method, it is supposed to block the entire piping channel, but in circumstances when the water current is too strong and washes away even the biggest granule in the piping channel, the granules will not be able to subside and get accumulated to perform the expected blocking. Therefore a better solution is needed.